This invention relates generally to shoe inserts and in particular to a laminated shoe insert and a laminating method.
Inserts are added to shoes to provide better support and comfort to the wearer. They may be used with virtually all types of shoes, from high performance athletic shoes to special orthopedic shoes or casual shoes. Inserts are typically made by the expansion molding of polyurethane-type materials. For example, a polyurethane foam is poured into a mold where it expands in an exothermic reaction to form an insert having the shape of the mold cavity. Sometimes a sock-lining fabric is put in the mold on top of the polyurethane foam and is bound to the foam as the foam exothermically expands and cures in the mold.
Since different regions of the sole of the foot are subject to different forces, it is desirable to make shoe inserts having regions of differing durometer or density to provide localized regions of support, shock absorption and cushioning. For example, it is sometimes desirable to have a greater degree of support in the heel area. One way to accomplish this is to vary the thickness of the expansion molded shoe insert making the heel region thicker than the other regions. Another way is to combine the expansion molded foam with a structural support member. For example, a preformed heel support may be glued or otherwise attached to the insert after the insert is formed. Alternatively, the preformed heel support may be secured to a sock-lining fabric and then the heel support and fabric may be placed in the mold together with the polyurethane foam. The heel support and fabric are then attached to the polyurethane foam during the exothermic reaction in the mold. Likewise, sheets of various porous products such as Poron and Latex have been exothermically bound to polyurethane foam as the foam cures in the mold to provide the shoe insert with better shock distribution and comfort. Again, a fabric is bound to the formed sheet of Poron or Latex and then the combination is placed in the mold with the foam.
The prior art has several drawbacks. Most notable is the unacceptable variation in the size of each insert manufactured according to exothermic expansion molding techniques from the same mold. Inserts manufactured according to typical methods have thicknesses that may vary up to 30%. However, many shoe manufacturers require less than 8% variation in the thickness of inserts for a particular size shoe to insure a properly fitting shoe or pair of shoes. The degree of variation in the thickness of shoe inserts made according to the prior art can result in the rejection of as many as 50% of the inserts for a given size at great expense and waste to the manufacturer.
The prior art also does not provide an easy and reliable way of making a single shoe insert having a variable durometer and density. Varying the thickness of the polyurethane foam is unsuitable because the variance usually causes the fit of the shoe to vary accordingly. Strengthening the heel region by attaching a heel support to a premolded polyurethane shoe insert outside of the mold is costly and time-consuming. Attaching the heel support during the exothermic molding process is impractical since the foam has a tendency to flow around the heel making it difficult to properly locate the heel support.
Exothermically attaching a sheet of Poron or Latex to polyurethane foam in the mold also is problematic. The polyurethane foam tends to seep into the pores of and stiffen the Poron and Latex thereby reducing the usefulness of the Poron and Latex. The invention overcomes these drawbacks and has other advantages over the prior art.
It is an object of the invention to provide a method for substantially reducing the dimensional variation usually created when manufacturing shoe inserts.
Another object of the invention is to provide a novel method for making a shoe insert from sheets or layers of cellular thermoplastic foam.
Another object of the invention is to provide a method for making a shoe insert having logistically designated areas of varying preselected durometer and density.
Another object of the the invention is to provide a method for precisely controlling the placement of support, shock absorbing and cushioning members in manufacturing a shoe insert.
Another object of the invention is to provide a unitary shoe insert having a smooth surface and regions of varying density or durometer.
Another object of the invention is to provide a shoe insert made from sheets or layers of cellular thermoplastic foam.
Another object of the invention is to provide a shoe insert having a foam layer and a porous layer wherein the pores of the porous layer are substantially free of any foam.
Another object of the invention is to provide a method for predetermining the thickness, durometer and density of selected portions of a shoe insert.
According to the invention, a shoe insert has two layers of cellular thermoplastic foam. One layer is different in size, density or durometer from the other layer. The layers are laminated together in facing relation to form the laminated shoe insert by the application of sufficient heat and pressure after each of the layers had been formed as a separate unit.
Also according to the invention, a shoe insert has at least two layers, one layer being a cellular thermoplastic foam and the other layer being a material useful for imparting a desired characteristic to the shoe insert. The two layers are laminated together in facing relation to form a unitary insert by the application of heat and pressure after each of the layers had been formed as a separate unit.
Also according to the invention, a shoe insert is formed by positioning a first and second layer of cellular thermoplastic foam in face-to-face relation between two mold halves which together form a mold cavity, and compression molding the first and second layers together to form a unitary shoe insert having the shape of the mold cavity.
Also according to the invention, two preformed layers of cellular thermoplastic foam are placed in face-to-face relation between the two mold halves which together form a mold cavity and the two halves are brought together to heat compression-mold the two layers together to form a unitary article having regions of varying durometer or density and having the shape of the mold cavity.